The present invention relates to a composite sleeve roll constituted by hard alloys having high hardness, high Young""s modulus and high rigidity and its fabrication method. Further, the present invention relates to a roll for cold-rolling a cold-rolled steel strip such as a stainless steel strip, a silicon steel strip, a bright finish steel strip or the like and to a rolling roll capable of producing a cold-rolled steel strip having a small amount of edge drop, a cold-rolled stainless steel strip and a bright finish steel strip having excellent surface brightness and a silicon steel strip having excellent magnetic properties with high advantage.
In the production of steel strip, steel wire or rod steel, for example, Sendzimir mill roll, wire mill roll and the like are used and with requests for high grade formation of steel material to be handled, energy conservation and so on, rolls with a material of hard alloys having high hardness and high Young""s modulus and excellent in wear resistance have been developed and used. These hard alloys rolls are mainly small-sized rolls having a comparatively small diameter, for example, a roll diameter of about 20 through 80 mm, or a roll diameter of 50 through 150 mm and a roll length of about 100 through 200 mm in accordance with a shape of material to be handled. In recent years, large size formation of hard alloys rolls has been requested in view of quality improvement of steel material and a necessity for long time period continuous operation for reducing production cost.
Generally, a monolithic body of hard alloys is used in a Sendzimir mill roll mentioned above and a wire mill roll or the like is fabricated by exerting compressive force in an axial direction to a shaft portion and a sleeve having an inner diameter substantially equivalent to a diameter of the shaft portion and surrounding the shaft portion as a central axis or exerting compressive force in a circumferential direction by a wedge type ring or the like to thereby fixing the sleeve onto the shaft portion and carrying out surface-finish treatment thereon.
However, according to the conventional method of fabricating a composite roll in which such a sleeve made of hard alloys is fitted to the shaft portion, in fabricating a large-sized roll (normally referring to a roll having a diameter of 150 mm or more and a length of 500 mm or more), the sleeve is fabricated by subjecting metal powder of hard alloys to rubber molding, sintering the metal powder as one piece hollow member having a hollow central shaft portion (with a diameter equivalent to the diameter of the shaft portion), subjecting the sintered body to hot isostatic press (HIP treatment) and thereafter machining the pressed body. Although the fabricated sleeve is fixed to the shaft portion, the hollow member is large-sized and is particularly made of the material of hard alloys and therefore, there cause frequently cases where large strain is generated in the material in subjecting the material to a heat treatment such as sintering or the like which makes difficult succeeding fabrication. Further, although in forming the hollow member by rubber molding, metal powder of hard alloys is packed sufficiently densely around a core rod having a diameter equivalent to that of the shaft portion and thereafter the core rod is drawn out to thereby form a mold body, when the hollow member is large-sized, the core rod is difficult to draw out and there pose frequently problems where the shape of the mold body is significantly deteriorated, a force more than necessary is needed and the like thereby causing difficulty in operational performance.
Next, an explanation will be given of a method of fabricating a cold-rolled stainless steel strip and a description will be given of problems in a method of fabricating stainless steel strip when large-sized rolls are used. Conventionally, a cold-rolled steel strip of stainless steel has been fabricated by the steps of annealing and pickling a hot-rolled strip, cold-rolling the hot-rolled strip by a Sendzimir mill or the like using a work roll made of a steel series alloy having a work roll diameter of 150 mmxc3x8 or smaller, subjecting the cold-rolled material to finish annealing and pickling or finish bright annealing and rolling the annealed material by finish temper rolling with a reduction ratio of 1.2% or less. The cold-rolled stainless steel strip fabricated through these steps is frequently used with a surface thereof as fabricated in the case of a ferritic stainless steel represented by, for example, SUS 430 and excellent surface brightness is requested in a product after having been subjected to the finish temper rolling. Meanwhile, in the case of an austenitic stainless steel represented by SUS 304, buffing is frequently carried out after the finish temper rolling and excellent surface brightness needs to be shown after the buffing. In the meantime, in recent years, in order to efficiently fabricate the cold-rolled stainless steel strip, a method of continuous cold rolling in one direction by a tandem cold mill using large-sized work rolls of 150 mmØ or larger is being adopted. For example, Japanese Unexamined Patent Publication No. 8-39103 discloses a technology in which work rolls of WC series hard alloys are used in at least one stand in a tandem cold mill by which production efficiency is promoted and surface brightness of cold-rolled stainless steel strip is promoted. However, according to the method, there pose problems in which not only the surface brightness of the cold-rolled stainless steel strip has yet to reach a sufficient level but also the surface brightness is deteriorated with rolling time period or a work roll may be broken under certain circumstances. Further, there poses also a problem in which the cost per se of the roll is high.
Next, an explanation will be given of a method of producing a grain-oriented silicon steel strip and a description will be given of problems when the grain-oriented silicon steel strip is produced by using large-sized rolls. Conventionally, a cold-rolled steel strip of grain-oriented silicon steel has been fabricated by the steps of annealing and pickling a hot-rolled steel strip, successively cold-rolling the pickled strip by a tandem mill using high alloy steel work rolls by twice or more interposing intermediate annealings and thereafter subjecting the rolled strip to decarburization annealing and finish annealing. It is known that when the silicon steel strip fabricated through these steps is cold-rolled without removing scale after the intermediary annealings, the surface roughness of the steel strip is enlarged and adverse influence is effected on magnetic properties. Therefore, grinding is carried out by using a grinding belt after the intermediary annealing and before the successive cold-rolling. Further, the grain-oriented silicon steel strip is provided with extremely high deformation resistance since 2.5 through 4.0 wt % of Si is normally added and when the rolling is carried out under high load and high surface pressure, there pose problems in which the rolls are made eccentric, the cylindrical shape cannot be maintained, in respect of the shape of the steel strip, edge drop is particularly enlarged, trimming margins on both ends of strip are increased and the yield is deteriorated. Further, according to the conventional rolls, there pose problems in which not only the surface roughness of the grain-oriented silicon steel strip after cold-rolling has yet to reach a sufficient level but also the surface roughness is deteriorated with the rolling time period or the work roll may be destructed under certain circumstances. Further, there poses also a problem in which the cost per se of the roll is high.
Firstly, it is an object of the present invention to provide a method of fabricating a composite sleeve roll having no strain of material mentioned above with excellent operational performance when a composite sleeve roll having high hardness and high Young""s modulus and excellent in wear resistance and long large-sized rolls are fabricated by using a material of hard alloys.
Further, there have been methods as technologies similar to portion of the present invention as disclosed in Japanese Examined Patent Publication No. 5-55202 and Japanese Unexamined Patent Publication No. 61-14104. However, Japanese Examined Patent Publication No. 5-55202 discloses a composite roll in which a sleeve produced by sintering powder of hard alloys or high speed steel at outside of a cylinder made of steel by high temperature hydrostatic molding by which the powder is subjected to diffusion bonding with the cylinder made of steel, and an arbor made of steel are fitted to each other, which is a roll for hot-rolling wire or rod steel and no mention is given to conditions for promoting surface brightness in cold rolling. Further, according to the disclosure in Japanese Unexamined Patent Publication No. 61-14104, although there has been disclosed a method in which a sleeve is molded by high temperature hydrostatic molding and a canning material on the inner side and the""sleeve are subjected to diffusion bonding by which the canning material is metallurgically bonded by middle build up process, the method is also in respect of a roll with an object of only improving wear resistance and skin roughening resistance and no proposal has been given of conditions of an outer layer portion of the roll constituting a rolling face and the like.
Hence, it is an object of the present invention to provide an inexpensive roll for cold rolling for resolving the above-described problems incorporated in the conventional technology and capable of further promoting the surface brightness of a cold-rolled stainless steel strip and a bright finish steel strip or the surface roughness of a silicon steel strip and stably rolling the above-mentioned cold-strips.
It is other object of the present invention to reduce edge drop of a cold-rolled steel strip, particularly to be able to achieve further promotion in the surface brightness of a cold-rolled stainless steel strip and a bright finish steel strip as well as the surface roughness of a silicon steel strip, to reduce a decrease in the surface brightness or the surface roughness even when rolling is carried out for a long period of time and to promote magnetic properties of the silicon steel strip. Further, it is other object thereof to provide an inexpensive roll for cold rolling without causing trouble such as breakage of roll or the like.
It is still another object of the present invention to provide a roll for cold rolling particularly achieving an effect by using the above-described respective features in a tandem cold mill.
Further, there have been proposed technologies similar to portions of the present invention in Japanese Examined Patent Publication No. 5-55202, Japanese Unexamined Patent Publication No. 4-41007 and Japanese Unexamined Patent Publication No. 60-111704. Further, a material having high Young""s modulus is a brittle material such as ceramics or hard alloys and there is a concern that when stress is concentrated during rolling, destruction is caused from the place of stress concentration. Accordingly, it is important to prevent stress concentration in the material during rolling. The technology disclosed in Japanese Unexamined Patent Publication No. 4-41007 proposes a method of preventing the stress concentration. According to the method, ceramics or hard alloys is used in an outermost layer of a rolling roll and an intermediary material is arranged between the outermost layer and a core material with an effective elastic modulus of 3000 through 17000 kgf/mm2 by means of fabricating grooves in a sawtooth shape in respect of oxygen free copper that is an elastoplastic material, winding the intermediary material in a form of a copper wire or the like. However, according to the rolling roll, when, a material for rolling having an extremely high deformation resistance as in, for example, a stainless steel strip or a silicon steel strip, is rolled under high load and high surface pressure, there is a concern in which the roll is made eccentric or the cylindrical shape cannot be maintained by plastic deformation of the intermediate layer and further, when the rolling continues the roll is destructed causing a serious problem.
Further, Japanese Unexamined Patent Publication No. 60-111704 has proposed a rolling roll which is a rolling roll having a roll barrel made of hard alloys and a roll neck made of steel and an intermediary material made of hard alloys having an amount of including a binder higher than that of the hard alloys of the roll barrel and having a higher strength, is provided between the roll barrel made of the hard alloys and the neck made of steel by soldering. However, no description has been given of the material of the hard alloys and further, a significant reduction in the cost in the case of fabricating a large-sized roll has not been resolved at all since a total of the roll barrel is constituted by the hard alloys.
Hence, it is an object of the present invention to resolve the above-described problems incorporated in the conventional technology and to provide a roll for cold rolling capable of further promoting the surface brightness of a cold-rolled stainless steel strip or a bright finish steel strip or to reduce the surface roughness of a silicon steel strip or to reduce edge drop and capable of stably rolling the cold-rolled steel strips such as the stainless steel strip, the silicon steel strip and so on.
It is other object of the present invention to provide an inexpensive roll for cold rolling capable of reducing edge drop of a cold-rolled steel strip, achieving further promotion in the surface brightness of particularly a cold-rolled stainless steel strip or a bright finish steel strip, or reducing the surface roughness and achieving further promotion in magnetic properties of a silicon steel strip without causing roll breakage or the like.
It is still further object of the present invention to provide a roll for cold rolling achieving an effect particularly when the above-described respective features are used in a tandem cold mill.
Further, generally, rolling oil is supplied as a lubricant between a steel strip and a roll in cold rolling of a steel strip. Therefore, a large amount of the rolling oil and metallic abrasive powder caused by friction between the roll and the steel strip in the rolling operation remain on the surface of the steel strip after rolling. When these are subjected to annealing at a succeeding step without cleaning them, the metal powder fixedly remains on the surface of the steel strip as it is or as it has been oxidized and nonuniformity of oil burn, oil stain or the like is caused on the surface of the steel strip whereby the surface quality of the steel strip is significantly deteriorated. Furthermore, when the nonuniformity is caused in a steel strip for an automobile or the like, partial exfoliation of deposit is caused in a succeeding plating step resulting in a failure in quality. Accordingly, there have been developed various technologies for cleaning the surface of the steel strip before the annealing step. For example, such a technology has been disclosed in Japanese Unexamined Patent Publication No. 60-261609, however, the technology is not yet sufficient. However, by carrying out cold rolling by using the roll of the present invention, that is, by using a WC series hard alloys which is difficult to adhere to a steel strip as the material of a rolling roll, occurrence of wear powder can be restrained, nonuniformity of the surface of the steel strip after annealing is not caused and a steel strip having surface cleanness more excellent than that in the conventional technology can be obtained.
The present invention relates to a composite sleeve roll and its fabrication method characterized in that it is a roll comprising a shaft portion and a sleeve having a hollow portion with an inner diameter substantially equivalent to a diameter the shaft portion and disposed at a surrounding the shaft portion in which the sleeve and the shaft portion are fixed to each other by inserting and fitting the shaft portion into the hollow portion and the sleeve is a sleeve constituted by previously integrating a plurality of pieces of formed body members divided by a face intersecting with the central axis of the roll.
Further, according to the present invention, in a composite roll for cold-rolling a stainless steel strip or a silicon steel strip in which a core member and a sleeve are fitted together, the core member comprises steel, a material of the sleeve comprises a WCxe2x80x94Co series hard alloys having Young""s modulus of 35000 kgf/mm2 or more and a Co content of 12 through 50 weight % and a wall thickness of the sleeve is formed to be 3% or more of a radius of the composite roll.
Further, according to the present invention, in respect of the above-mentioned invention, it is further specified that a ratio L/D of a length L of a barrel of the sleeve to a diameter D of the roll falls in a range of 2 through 10.
Further, according to the present invention, there is provided a composite roll for cold rolling in which a roll barrel comprises three or more of layers in shapes of concentric circles, an outermost layer is provided with Young""s modulus of 35000 kgf/mm2 or more and a thickness of the layer of 3% or more of a radius of the roll and an intermediate layer disposed between the outermost layer and a shaft core is provided with Young""s modulus which is smaller than the Young""s modulus of the outermost layer and larger than Young""s modulus of the shaft core.
Further, according to the present invention, it is preferable that in respect of the above-mentioned invention, when the intermediate layer comprises two or more layers, materials of the intermediate layers are arranged such that the more relatively outer side the layer is disposed, the higher Young""s modulus is provided to the material.
Further, according to the present invention it is preferable that all of the outermost layer and the intermediate layers comprise a WC series hard alloys and the composition of the hard alloys is constituted such that the more relatively outer side the layer is disposed, the smaller an equivalent bond amount of a binder metal is constituted.